Insulation test set



Jan. 9, 1945.

R. M. EDMONDS 2,367,013

INSULATION TEST SET Filed March 24, 1942 INVENTOR [Emma/dais BY S ATTORNEY Patented Jan. 9.1945

UNITED s'rA'rss PATENT OFFICE INSULATION TEST SET Robert Mason Edmonda, Elmira, N. Y., assignor to American Telephone and Telegraph Company, a corporation of New York Application March 24, 1942, Serial No. 436,011

- 9 Claims. ((1179-1753) cuit, to determine whether or not the resistance to ground of the isolated conductor is greater than a predetermined value. This prior arrangement of separately studying each telephone conductor is a slow and costly process and is of little value where insulation tests must be made rapid- 1y over hundreds of conductors during periods when wet weather conditions prevail.

Accordingly it is an object of the present invention to provide a testing arrangement for rapidly determining which of the two conductors of a telephone or other line is grounded, and at thesame time determine whether the two conductors of the line are short-circuited to each other.

Another object of this invention is to provide a testing arrangement involving two detecting devices so set up that one of the detecting devices will be operated only when the resistance to ground of one of the conductors of a line is less than a predetermined value and the other detecting device operated only when the resistance to ground of. the other conductor of the line is less than the same predetermined value.

It is a further object of this invention to have both detecting devices operated when the two conductors of the line are short-circuited to each other.

to so arrange the testing apparatus that inconI' necting the testing apparatus to a telephone line the presence of a busy condition on the line I of the conductors of the line to be tested. When the insulation to ground of either of the conductors of the line is below a predeterm n d va In". the voltage supplied to the battery in the same branch will be suflicient to fire the associated gas tube. Each gas tube circuit also includes an in dicating device to indicate that the correspondinggas tube has been fired. Thus each branch of the testing system separately detects the'pres- And it is a sun further object of this inv'entionf just referred to.

ence of lowlinsulation resistance to ground of 7 but one of the'line conductors. An additional circuit is superimposed on the testing arrangement, this circuit including another indicatin device, such as a lamp, which will become operated only when the two conductors of the telephone line are "busy."

This invention will be better understood from the more detailed description hereinafter following when read in connection with the accompanying drawing showing one embodiment of the invention merely for the purpose of illustration.

Referring to the drawing, the reference characters T1 and T2 designate two three-electrode gas tubes of the cold cathode type which are connected in the two branches of the testing system to be described. The input electrodes of the tube T1 are connected in a circuit including resistors R1, R2, R3 and R4, the resistor R4 being adjustable for calibrating purposes. Likewise the input electrodes of the tube T2 are connected to a similar circuit including resistors R5, R6, R7 and R2, the resistor R5 being likewise adjustable for calibrating purposes.

The resistor R2 is, of course, common to the two circuits or branches The upper terminal of resistor R4 is connected to the tip terminal of a jack J1 by means of a battery B and a similar battery B2 which is of opposite polarity but of like potential is connected between the lower terminal of resistor R6 and the ring terminal of jack J1.

The primary winding ofv transformer W is connected between an alternating current generator G and ground. This primary winding is also con nected in circuit with the anode of tube T2 and its upper input electrode through the winding of a buzzer designated Z2 which is of well known type. The secondary winding of transformer W which may have the same number of turns as the primary winding' -is'connected in circuit with the ar'iodejoftube'Ti -an'd itsupper input elec'-' trodethroughthe winding of a buzzer designated Z1. It will be apparent that the buzzer Z1 will be operated only when the gas tube T1 is fired,

and that the buzzer'Z: will be operated only when the gas tube T2 is fired.

The drawing also shows a-special patch cord' including two plugs P1 and P2 of well known types. The tip and ring contacts of plug P1 may, of course, engage the tip and ring terminals of the jack J1 in the usual manner, the sleeve terminals of the two plugs P1 and P2 being connected in a circuit which includes a lamp L for determining the busy condition of each line to be tested as will be explained hereinafter. The plug P2 may engage the line C1-C2 to betested. the connection being established for example, through a jack J2 which may be part of the test connector of a step-by-step central oflice system thetestbelnaemployedfor e terminalsofjackJrandplugPnthefiptermiroutinetestins H tstobeperi'ormedby nals of plug Pa and jack J2, conductors C1 and theapparahnoitbisinvmflon. Onlyoneotthe Catheringterminalsofjackhandri shthe Jacksofthetesteonnectorhasbeenshownfor ringterminalsorplugPrandjaekJi,batteryBz, ilhistraflvepnrposes. -Thetwouppertermlnals l resistorsReandlt-randresistorsmandm. The ortheiaekhmcteumwiredtotbetwo ,iloworcurrentthrouahresistorsmandmwill eonductorscrandchotthetelephoneorother besumcienttoapplvavoltagethroughresistors wellknowniwn Assumethatthepluehhasjaekh andthatplugPzhasthetestconnector jack J: otfhecentral oillce system,andthat.a routinetestistobemadetodetenninethe 'insulation conditions of the conductors C1 and C: oroneofthetelephonelinesofthesystem. It theinsulationcetogroundottheconductorciis'lessthanapvalue, current will flow from battery 131 over conductor C1 through its insulation resistance, the interconnected circuit including ground, resistors Rs, Rzand RebattervBnthetipterminalsor jack J1andplugP1.thetipterminalsofplugP:and jack J: and the conductor 01 (includingtbepath through the insulation of the latter conductor havingalowresistancetoground). Thiscurrentwillestablishapotentialacrosresistorslta, RaandRewhichissumcie'nttoloniae theg:

0 fliattheinsulationoftheeonduetcr C1 is below the value for satisfactory operltion. Thevoltasetooperatethecircuitotbuznerzl isobtainedrromthewindingotuansiormerw.

Ontheotherhandjitheinsulationresistance oftheconductor C: ofthetelephonelinebeing tested is below the predetermined value previouslyestablisheicurrentwillthenflowrrom batterylhoveracircuitwhichincludesgroimd, resistorsltgRwandRebatterymtheringterminalsofjack-lrandplmietberingterminals ofplugPzandjaek-lzandcmiductorcafincludingtheleakagepathtogroundflunconductor C1). ThecurrentflowthroughresistorsR.:,R-: andRsissuchastoapplyavollagethroughr-esistorRstotheinputelectmdesortubeTato ioniaethegastherein. Upmionhntionotthe gasoftube'l'athebumerzzwillheoperamthe operated circuit generator G, the windingofbumerzgtheanodeanduppereathodect wbeT:andground.,'1hustheoperatorwll1be instantlyiniormedthattheconductorcrotthe linebeingtestedhasaninsulationwhichdoesnot meetthestandardofgoodservioe.

Thusitwillbethatmeotthetwo gastubeswillbeflredlndilscmnectedbm willbeoperatedwhenoneoithetwoconductors otatelephonelinehasaninslflationreslstance togroimdbelowavalue. The gastubeicnimedandthebuneroperatedwillindicatewhiehofthetwoconduetorais fanlty- SupposenowtbattheCrandC: areshort-circuitedtoeashother,orthattheresistanoeorisbelowsmne value. InfllateventthetwobatteriesBrandflswillbeingerieswith eachothertotheconductursciandfithemteb connected circuit including battery B1,

R1 andlhtothelmaitelectr'odesoftube'hto ioniaethegas'thereinandtherebyoperatethe buzaerzi. Idkewisetheflowofcurrentthrmmh resistorsReandll-lwillbesmilcienttoapplya voltaaethroughRaandRstotheinput electrodesortube'l'ztoioniaethegasthereinand therebyoperatethebulaerzi. 'l'husitwillbe observed that the of a shirt-circuit across the telephone conductors C1 and C: will resultlnbothtubes'lrand'lzbeingflredand bothblmersziandzabeingoperated. Thiscondiflon will. therefore-be readily distinguished 1mm the previous conditions in which but one otthe conductors had aninsulation resistanceto ground belowsmnepredetermined valueinwhich casebutonegastubewasflredanditseoneq runn; buzzer operated.

ItwillbeobservedthatthelarnpLisinthe sleevecircuitofthetestingsystemandthatitis connectedto the sleeve conductor 0: atthecentralofllce. Thislampwillbelightedwhenthe conductorsclandczotthetelephonelineare notbusybecauseinthateasetheconductorca will have a voltage applied thereto suillcient to operate thebusylampL. Thecircuit for lamp hwillincludetheconductorcsandthebattery (not shown) connectedthereto,thesleeve terminalsofjackJzandplughthelamp sthesleeve terminalsotpluzlrandjackhandgroumi. In the event, however, that the telephone line which includes conductors C1 and Caisbusmthe battery voltage just considered will be removed from the conductor C: due to the .operafion of the cut-oi! relay (not shown) at the central ofiice, and then no current will flow through the lampL. ThusthelampI-willbellghtedonly whenthetelephonelineisnotbusy. Thetest operatorwmthereforebeahletodetermineinstantlywhetheaornotthelinebeingtestedis busy. Indicationsobtainedbythetestapperatus frmnabusylinewill,ofcomse,beignoredbecametheeeoftheconductorsotthelineareatthattimeconsiderably changedrromtheirnormalvalues.

Inoneinstallatiminwhichthecimmtofthis hivuiiionwasusedthebatteriesBiandBzwere oItheM-volttypeandthetubes'hand'hwere oifthemdtype. Suchvoltageswillnotbesmtableformeonlineseonnectedtofour-partygas tubeaets. 'l'omtisfactorilvtestthelinesofsueh setsbatteriesoflowervoltagesmaybeemp oyed. Iffi-voltbatferimareuseithenthetubes'h and'lbmaybe,forexample,ofthethyratron typ In making tests with the apparatus of this invention it may happen that either or both of the gas tubes will be fired and the corresponding bmners operated only momentarily. This transient condition is usually brought about/by the capacity between the conductors of the line. by the capacity of the condensers in the subset. etc- This capacity may be suflicient to allow a transient current to flow over the line conductors and through the testing circuit. Such a transient reaction is not an indication of low insulating reslstance in either or both of the line conductors unless the indication fails to stop. The appathe tip 15 ratms of this invention is intended 10 indicate a cating devices such as buzzers Z1 and Z2 respectively. It will be understood that the buzzers Z1 and Z2 may be omitted if desired and that tubes T1 and T2 may be'employed to act as visual indicators. In the latter situation one of the tubes may be painted red, for example, and the other green.

It will be understood that the testing circuit of this invention may be used with any form of signaling or other circuit. It will also be understood that any one or all of the plugand jack arrangements shown herein may be omitted if so desired and other means may be provided for establishing connections to the circuit or circuits to be tested. While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit of the invention and the, scope of the appended claims.

What is claimed is:, g

1. Apparatus for determining which of the two conductors of a telephone line has an insulation resistance to ground below a predetermined value, comprising two batteries, two circuits, each of which is conductively connected to one of the conductors of the line and one of the batteries, two gas tubes which are normally inert, each of which is associated with one of the batteries and one of said conductors, means responsive to the grounding of one ofsaid conductors to initiate the flow of current from the corresponding battery to ionize the associated gas tube, and two indicating' devices controlled respectively by said gas tubes.

2. Testing apparatus for a; two-wire line to determine which of the two conductors of the twowire line has an insulation resistance to ground below a. predetermined value, comprising two equal sources of voltage each of which may be connected conductively to one of the wires of the line, two gas tubes which are normally inert, two

networks respectively interconnecting the two gas tubes to the two sources of voltage respectively, means responsive to the grounding of one of said wires to initiate the flow. of a substantial current from the corresponding source of voltage v to ionize the respective gas tube connected thereto, and means to indicate which of the has become ionized.

3. Testing apparatus for a two-wire line, to determine which of the two'conductors or the twowire line has an insulation resistance to ground below a predetermined value. comprising two equal sources of voltage each of which may be connected conductively to one of the. wires of the gas tubes line, two gas tubes which are normally inert, two

networks respectively interconnecting the two .gas tubes to the two sources of voltage respectively, means responsiveto the drop in the insulation resistance to ground ut one of the wires of said line to initiate flow of a substantial current ing the time when the gas within the two tubes is from the corresponding source of voltage to ionize the respective gas tube connected thereto.

4. Testing apparatus for a two-wire line to determine which of the two conductors of the twowire line has an insulation resistance to ground belowa predetermined value, comprising two gas tubes each of which is normally inert and is conductively connected to one of the wires of said line, means for firing either of said tubes when the wire connected thereto becomes grounded, and means for firing both tubes when the two wires are short-circuited to each other.

5. Testing apparatus for a two-wire line to determine which of the two conductors of the twowire linehas an insulation resistance to ground below a predetermined value, comprising two gas tubes which are normally inert, two networks each including a separate source of potential, said networks respectively conductively interconnecting said two tubes with the two wires'of said line,

means responsive to a grounded condition on either of said wires to fire the respective gas tube, connected to the grounded wire, and means responsive to ashort-circuit between said wires to simultaneously fire both gas tubes.

6.'Testing apparatus for a two-wire telephone line comprising two gas tubes which are normally inert, means responsive to a short-circuit between the wires of said line to ionize the gas within both tubes simultaneously, and further means for indicating whether the telephone line is busy durionized.

7. Testing apparatus for telephone lines comprising two sources of potential, two resistors connected in series with each other and with said sources, said series circuit including the nearend terminals of a telephone line to be tested, two gas tubes which are normally inert and are connected respectively across said resistors, and

means for indicating whether either or both of said gas tubes have been fired.

8. Testing apparatus for a two-wire line to determine which of the two conductors of the twowire line has an insulation resistance to ground below a predetermined value, comprising two equal sources of potential, two resistors having a common grounded terminal, each resistor-being conductively connected to one of the wires of said line through one of said sources of potential, and two gas tubes each of which is normally inert and is bridged across one of said resistors, said gas tubes being fired when the voltage across the respectivev resistors exceeds a predetermined potential.

9. Testing apparatus for a two-wire line to determine which of the two conductors of the twowire line has an insulation resistance to ground below a predetermined value, comprising ,two equal sources of potential, two resistors having a commongrounded terminal, each resistor being conductively connected to one of the wires of said line through one of said sources of potential, and

two gas tubes each oi which is normally inert and 4 is bridged across-one of said resistors, said gas tubes being flred when the voltage across the respective resistors exceeds a predeterminedqgalue, two indicating devices controlled respective y by said gas tubes',.and a source of alternating potential for operating both of said indicating devices.

monnrir MASON nnMoNns. 

